Modern semiconductor technology has created a high demand for structuring and probing specimens in the nanometer or even in the sub-nanometer scale. Micrometer and nanometer scale process control, inspection or structuring is often done with charged particle beams, e.g. electron beams, which are generated, shaped, deflected and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. For inspection purposes, charged particle beams offer superior spatial resolution compared to, e.g., photon beams because their wavelengths are shorter than the wavelengths of light beams.
Inspection devices using charged particle beams such as scanning electron microscopes (SEM) have many functions in a plurality of industrial fields, including, but not limited to, inspection of electronic circuits during manufacturing, exposure systems for lithography, detecting devices, defect inspection tools, and testing systems for integrated circuits. In such particle beam systems, fine probes with high current density can be used. For instance, in the case of an SEM, the primary electron (PE) beam generates particles like secondary electrons (SE) and/or backscattered electrons (BSE) that can be used to image and analyze a specimen.
One drawback of electron-beam based systems is the limited probe current within the focused spot. With increasing resolution (decreasing spot size), probe current is further decreased because of a reduced aperture angle required to control the aberrations. Higher brightness sources can provide only limited improvements for the probe current, because of the electron-electron interactions. Many approaches have been made to reduce e-e interactions in electron beam systems, which are, for example, reduced column length and/or higher column energy combined with late deceleration of the electron beam to the final landing energy just in front of the sample. However, improvement of single electron beam throughput at required resolution is increasingly challenging. One approach to solve such problems is the use of multiple beams, which may be generated by a single source within one column, which reduce the throughput by the number of beams.
Individually controlling, directing, deflecting, shaping, correcting, focusing, and steering the individual beamlets of such a multiple-beam system is, however, challenging. Electrostatic multipole deflectors and stigmators such as electrostatic octupole devices may be used for this purpose. However, it is difficult to sufficiently miniaturize electrostatic multipole devices and at the same time maintain excellent beam influencing properties and electrical field properties.
Further, also multipole devices for single charged particle beam systems may suffer from an insufficient quality of the electric fields which may lead to an increased spot size and impair the achievable spatial resolution of charged particle which may provide excellent field qualities to be used for deflecting and correcting charged particle beams.